Various anchoring or restraint methods are known for securing automotive vehicles to a flat-bed transport vehicle to prevent shifting of those automotive vehicles during shipping from a manufacturing facility to a delivery location. A commonly used method is to tie the vehicles downwardly to the support surface, e.g. the floor of a railway flat-bed car, using chains which are tightened by ratchet mechanisms. An end of a chain is attached to the chassis or frame of the vehicle and a hook on the ratchet mechanism is attached to a hole in a steel runner or rail on the support surface. The ratchet is then actuated to tighten the chain and partially or completely compress the springs of the vehicle's suspension system. Normally, one chain and ratchet combination is positioned adjacent each of the vehicle's wheels.
In an attempt to decrease the length of time required to secure a vehicle to a flat-bed transport vehicle, wheel chocking devices have been developed. One example of a vehicle wheel chocking device is disclosed in U.S. Pat. No. 5,312,213. In general, wheel chocks are positioned in front of or behind each front and rear wheels and secured to some portion of the transport vehicle support surface. Such wheel chocks have been found to adequately restrain vehicles against horizontal movement with respect to the flat-bed, but do not restrain the body of the vehicle against bouncing on its own suspension system while the flat-bed is in motion. Such bouncing can cause wear and tear on the suspension system during pre-delivery shipping of the vehicle.
More significantly, unrestrained bouncing of the vehicle may cause damage to the vehicle body. Automotive vehicles are often transported on double-decker railway cars to permit carriage of twice as many vehicles as would be possible on a single deck car. It has been found that bouncing of the vehicles can be severe enough that the vehicles carried on the lower deck strike the underside of the upper deck above them, causing significant damage to the roof of the vehicle. This is most commonly a problem for tall vehicles, such as full-size vans.
To prevent bouncing of the restrained vehicles, attempts have been made to use ratchet tie-down mechanisms along with wheel chocks. It is, of course, possible to use the expensive and cumbersome chain-and-ratchet devices employed previously and which the wheel chocks were intended to replace. For reasons of lower cost and greater ease and safety during use, it would be preferable to use a restraint system that employs woven, synthetic webbing straps. Such ratchet-and-strap devices are used in a wide variety of industrial applications, and are procurable off-the-shelf for a relatively low price.
Unfortunately, it has been found to be very difficult, when using an off-the-shelf ratchet mechanism, to generate enough leverage to tighten the restraint straps to the point where they completely compress or "bottom out" the suspension of the vehicle. During tests conducted with General Motors Corporation 3/4-ton and 1-ton vans, the best that can be achieved in normal operating conditions is to compress the suspension approximately 21/2 inches out of a total travel of approximately 4 inches. Accordingly, while the straps are able to restrain the vehicle against bouncing upward and so prevent the top of the vehicle from striking the overhead structure of the transport vehicle, some degree of bouncing downwardly from the restrained position may still occur. This bouncing may at times be large enough in magnitude that a restraint strap can become sufficiently slack to allow the prior art hooks used to restrain vehicles to a transport vehicle (see FIG. 6) to come unhooked from the hole, eyelet, or other feature with which it is engaged.
Existing ratchet-and-strap restraint devices have also been found to be unusable in this environment because of failures of the webbing strap itself. When the ratchet mechanism is actuated to tighten the strap, the strap is wound in a spiral fashion around a shaft of the ratchet. During use to restrain a vehicle against vertical movement, bouncing of the vehicle subjects the strap and ratchet to a cyclical, tug-and-release type of loading. This results in the layers of webbing wrapped around the ratchet shaft sliding over one another with sufficient friction to cause heating within the spiral-wound webbing strap. Such heating may be of sufficient intensity and duration to melt and fuse the layers of webbing, preventing the strap from being unwound or even causing failure of the restraint strap during use.